Mechanical tests performed on specimens of new material--such as hardness, breaking, plasticity or elasticity tests--are governed by ISO international standards, which, for the test to be considered valid, require a minimum specimen size. In some cases, however, as in the case of materials produced in nuclear reactors or particle accelerators, the amount of raw material produced may not be sufficient to form specimens of the prescribed ISO standard size.
By way of a solution to the problem, various nonstandard test methods have been devised for small-size specimens, most of which reproduce the standard methods on a smaller scale.
Particularly interesting nonstandard methods are those for testing disk-shaped specimens of 2-10 mm diameter and 0.1-1 mm thickness. A typical example is the so-called "punch test", wherein a concentrated load is applied to the central portion of a disk-shaped specimen secured about its peripheral edge, and deformation of the disk is measured to determine the mechanical characteristics, e.g. resistance, ductility, hardness and anelastic performance, of the material. The same type of test conducted up to the breaking point of the specimen provides for studying the fracture formation process prior to breakage.
Measurements of the above type, however, involve several problems, precisely on account of the small size of the specimen. That is, in addition to the difficulty encountered in securing the specimen firmly about its peripheral edge and applying the load in the exact center of the specimen, deformation of the specimen following application of the load is also difficult to measure to the required degree of resolution. Moreover, during application of the load, the small size of the specimen also produces end effects which may affect the reliability of the results.
The amount of deformation of the specimen is traditionally determined using known mechanical measuring devices, which, however, are limited as regards resolution and precision. Deformation of the specimen during testing may also be real-time controlled using optical image acquisition devices, such as a telecamera. In this case, however, the information supplied is difficult to process.